Current semiconductor laser elements or the like are formed collectively on a compound semiconductor substrate and thereafter each semiconductor laser element is cut out by cleavage. Each semiconductor laser element formed in this manner has the same structure. In this case, semiconductor laser elements in which diffraction gratings or the like are partly formed on the side of the end from which laser light is emitted are formed in a matrix form that each diffraction grating is arranged uniformly in the same direction on the semiconductor substrate 1 as shown in FIG. 11.
In each semiconductor laser element, a clad layer and an active layer of a semiconductor laser element are formed using semiconductor process technologies. After that, in FIG. 11, these semiconductor lasers are first cleft through cleavage planes C11 to C14 to form laser bar LB11 to LB13. Each cleavage plane of each of these laser bars LB11 to LB13 is subjected to coating to form a reflecting film and an emitting film collectively. Then, the laser bars LB11 to LB13 on which the reflecting film and the emitting film are formed are cleft every each of laser bars LB11 and LB13 corresponding to cleavage planes C21 to C24 to cut out a semiconductor laser element LD10 finally. For example, each semiconductor element is cut out as semiconductor laser elements LD11 and LD13.
FIG. 12 is a view showing a section along the line B—B corresponding to the cleavage plane C22 before the laser bars LB11 and LB12 are cleft and the section after cleft. As shown in FIG. 12, the laser bar LB11 is cut out by the cleavage of the cleavage planes C11 and C12 and the laser bar LB12 is cut out by the cleavage of the cleavage planes C12 and C13. Here, the cleavage plane C11 forms at least a reflecting surface HR11 of each semiconductor laser element forming the laser bar LB11. Also, the cleavage plane C12 forms an emitting surface AR11 of the laser bar LB11 and also a reflecting surface HR12 of the laser bar LB12. Further, the cleavage plane C13 forms at least an emitting surface AR12 of the laser bar LB12.
In the semiconductor laser element LD11 formed in the laser bar LB11, a diffraction grating G11 is formed on the side of the emitting surface AR11 and in the semiconductor laser element LD12 formed in the laser bar LB12, a diffraction grating G12 is formed on the side of the emitting surface AR12. The position of each of the diffraction gratings G11 and G12 is aligned with high accuracy on the basis of a pattern of a mask aligner aligned based on an orientation flat OF by using semiconductor process technologies. On the other hand, the cleavage planes C11 to C14 and C21 to C24 are also cleft one after another by a scriber after scratches are formed at positions corresponding to the cleavage planes C11 to C14 on a part of the semiconductor substrate 1 by using a diamond cutter.
However, the aforementioned cleavage planes C11 to C14 are not always cleft along a straight line but there is a case where a misregistration of the order of μm arises depending on the type of crystal surface. Also, though the surface of the orientation flat OF is formed with high accuracy by polishing, there is a case where an angle misregistration of, for example, ±0.05 degree arises. In this case, the misregistration of the cleavage planes C11 to C14 arises resultantly. Also, a misregistration of the order of μm arises due to the effect of the warpage of a semiconductor wafer during the course of mask alignment.
When such a misregistration of the cleavage planes C11 to C14 arises, misregistrations of the diffraction gratings relative to the semiconductor laser elements LD11 and LD12 arise in the semiconductor laser elements LD11 and LD12 as shown in FIG. 13 and FIG. 14. In FIG. 13, actual cleavage planes C11′ to C13′ are shifted towards the orientation flat OF side from the proper cleavage planes C11 to C13 (shifted to the left side on the figure). Specifically, the cleavage planes C11 to C13 are shifted to positions which encroach upon the inside of each of the diffraction gratings G11 and G12. As a result, in the semiconductor laser elements LD11′ and LD12′ corresponding to the semiconductor laser elements LD11 and LD12, diffraction gratings G11′ and G12′ having shorter lengths of diffraction gratings than those of diffraction gratings G11 and G12 are formed and diffraction gratings g11 and g12 which are parts of the diffraction gratings G10 and G11 adjacent to the side of the reflecting film are formed.
In FIG. 14, actual cleavage planes C11″ to C13″ are shifted from the proper cleavage planes C11 to C13 respectively to the side opposite to the orientation flat OF (shifted to right side on the figure). Specifically, the cleavage planes C11 to C13 are shifted to positions apart from each of the diffraction gratings G11 and G12. As a result, in semiconductor laser elements LD11″ and LD12″ corresponding to the semiconductor laser elements LD11 and LD12, a space where no diffraction grating is formed between the facets of the emission sides and emission films of the diffraction gratings G11 and G12 is produced.
From these results, in the manufactured semiconductor laser elements, a diffraction grating having a desired diffraction grating length is not formed but unnecessary diffraction gratings are formed or diffraction gratings are not placed on desired positions, giving rise to the problem that there is the case where neither desired oscillation wavelength nor desired laser output can be obtained, causing reduced yields.
It is to be noted that the shifts of the cleavage planes C11 and C13 are not limited to the shifts in the same direction and there is the case where cleavage planes C11 to C13 are individually shifted independently. Also, there is the case where no straight cleavage plane is formed during the course of cleavage so that each of the cleavage planes C11 to C13 itself is shifted depending on the crystal plane.